Filter systems including patterned optical analyte sensors and optical readers

ABSTRACT

A filter system includes a housing, a filter medium disposed within the housing, an optical analyte sensor, and an optical reader. The optical analyte sensor is characterized by a first region that exhibit a first response to an analyte of interest and a second region that exhibit a second, different, response to an analyte of interest. The optical analyte sensor includes a detection medium and is disposed within the housing such that the detection medium is in fluid communication with the filter medium. The optical reader includes at least one light source and at least one detector.

FIELD OF THE INVENTION

The present disclosure relates to filter systems that include a filtermedium, a patterned optical analyte sensor disposed in fluidcommunication with the filter medium, and an optical reader configuredand disposed to interrogate the patterned optical analyte sensor.

BACKGROUND

Filter systems are commonly used in the presence of vapors and otherhazardous airborne substances. Exemplary filter systems includecollective protection systems, disposable personal respirators, reusablepersonal respirators, powered air purifying respirators, haz-mat suitsand other protective devices.

Various chemical, optical or electronic indicators have been proposedfor warning users of protective devices of the presence of undesiredmaterials. For example, an end-of-service-life indicator (“ESLI”) canwarn that a filter element in such a device may be approachingsaturation or may be ineffective against a particular material.

The ability to detect chemical analytes, especially organic chemicalanalytes, is important in many applications, including environmentalmonitoring and the like. Some devices that have been used for detectionof chemical analytes have been developed, for example optical,gravimetric, microelectronic, mechanical, and colorimetric.

SUMMARY

In one exemplary embodiment, the present disclosure is directed to afilter system, including a housing, a filter medium disposed within thehousing, an optical analyte sensor, and an optical reader. The opticalanalyte sensor is characterized by a first region that exhibits a firstresponse to an analyte of interest and a second region that exhibits asecond, different, response to an analyte of interest. The opticalanalyte sensor includes a detection medium and is disposed within thehousing such that the detection medium is in fluid communication withthe filter medium. The optical reader includes at least one light sourceand at least one detector.

In some embodiments, the optical reader includes a first assembly and asecond assembly, each including at least one light source and at leastone detector. The optical reader may be attached to the housing suchthat at least a portion of light emitted by at least one light source ofthe first assembly is reflected from the first region of the opticalanalyte sensor and captured by at least one detector of the firstassembly, and at least a portion of light emitted by at least one lightsource of the second assembly is reflected from the second region of theoptical analyte sensor and captured by at least one detector of thesecond assembly. At least one of the first and second assemblies mayinclude a first block comprising a first light source and a firstdetector and a second block comprising a second light source and asecond detector.

In other embodiments, at least a portion of light emitted by at leastone light source is reflected from the first region of the opticalanalyte sensor and captured by at least one detector. In addition, atleast a portion of light emitted by at least one light source isreflected from the second region of the optical analyte sensor andcaptured by at least one detector.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing detailed description of various embodiments in connection withthe accompanying drawings, wherein:

FIG. 1 shows one exemplary filter system according to the presentdisclosure;

FIG. 2 shows a filter cartridge that may be used in filter systemsaccording to the present disclosure;

FIGS. 3A and 3B show schematically exemplary optical analyte sensorssuitable for use with some exemplary embodiments of the presentdisclosure;

FIG. 4 shows an exemplary optical reader according to the presentdisclosure;

FIG. 5A shows spectra of exemplary light sources of an exemplary opticalreader, as well as a spectrum of an exemplary optical analyte sensor inthe absence of a target analyte;

FIG. 5B shows a curve representing exemplary photodetector sensitivityto wavelength of incident light;

FIG. 6 shows schematically another exemplary embodiment of an opticalreader according to the present disclosure;

FIG. 7A shows an exemplary embodiment of an optical reader utilizing oneor more broadband light sources;

FIG. 7B shows schematically a filter having areas with differentspectral transmissions;

FIGS. 8A and 8B show different sides of an exemplary embodiment of anoptical reader according to the present disclosure;

FIG. 9A shows an exemplary optical reader according to the presentdisclosure, which is configured to interrogate a patterned opticalanalyte sensor;

FIG. 9B shows another exemplary optical reader according to the presentdisclosure, which is configured to interrogate a patterned opticalanalyte sensor;

FIG. 10 is a diagram illustrating the operation of optical readersaccording to the present disclosure;

FIGS. 11A-11D show schematically another exemplary filter systemaccording to the present disclosure and some exemplary components ofsuch a filter system;

FIG. 12 shows an embodiment of a removable housing portion according tothe present disclosure;

FIGS. 13A and 13B show exemplary embodiments of attachment mechanisms;

FIG. 14A-14C show schematically different types of registrationfeatures;

FIG. 15 shows yet another embodiment of a filter system according to thepresent disclosure;

FIG. 16 shows a respirator cartridge suitable for use in exemplaryembodiments of the present disclosure;

FIGS. 17A and 17B show yet another exemplary filter system according tothe present disclosure;

FIGS. 18A and 18B illustrate a suitable attachment mechanism that may beused in filter systems according to the present disclosure; and

FIG. 19 shows another exemplary filter system according to the presentdisclosure.

Like reference symbols in the various figures indicate like elements.Unless otherwise indicated, all figures and drawings in this documentare not to scale and are chosen for the purpose of illustratingdifferent embodiments of the invention. In particular the dimensions ofthe various components are depicted in illustrative terms only, and norelationship between the dimensions of the various components should beinferred from the drawings, unless so indicated. Although terms such as“top”, bottom”, “upper”, lower”, “under”, “over”, “front”, “back”,“outward”, “inward”, “up” and “down”, and “first” and “second” may beused in this disclosure, it should be understood that those terms areused in their relative sense only unless otherwise noted.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings that form a part hereof, and in which are shown by way ofillustration several specific embodiments. It is to be understood thatother embodiments are contemplated and may be made without departingfrom the scope or spirit of the present invention. The followingdetailed description, therefore, is not to be taken in a limiting sense.

All scientific and technical terms used herein have meanings commonlyused in the art unless otherwise specified. The definitions providedherein are to facilitate understanding of certain terms used frequentlyherein and are not meant to limit the scope of the present disclosure.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise. As used inthis specification and the appended claims, the term “or” is generallyemployed in its sense including “and/or” unless the content clearlydictates otherwise.

The present disclosure is directed to systems and devices that may beapplied to indicate an end of service life or provide a user withinformation related to an end of service life of a filter medium, suchas that of a respiratory filter or cartridge used in hazardousenvironments for protection against volatile organic compounds. It isexpected that the present disclosure will help provide a more accurateend of service life indication for various filter systems. It isenvisioned that some exemplary embodiments may be provided asaccessories for respirator cartridges and filters, while other exemplaryembodiments include entire respirators and cartridges. The presentdisclosure is applicable to various filter systems, such as personalrespirators, including powered air purifying respirators, reusablepersonal respirators, disposable personal respirators, haz-mat suits,collective protection filters and other applications that will befamiliar to those skilled in the art.

Exemplary embodiments of the present disclosure may be used to detectand/or monitor one or more analytes of interest. Such an analyte maycomprise a vapor or gas that may be present in an environment (often, anair atmosphere) that is desired to be monitored. In some embodiments,the analyte is an organic vapor (e.g., a volatile organic compound).Representative organic analytes may include, without limitation,substituted or unsubstituted carbon compounds including alkanes,cycloalkanes, aromatic compounds, alcohols, ethers, esters, ketones,halocarbons, amines, organic acids, cyanates, nitrates, and nitriles,for example n-octane, cyclohexane, methyl ethyl ketone, acetone, ethylacetate, carbon disulfide, carbon tetrachloride, benzene, toluene,styrene, xylenes, methyl chloroform, tetrahydrofuran, methanol, ethanol,isopropyl alcohol, n-butyl alcohol, t-butyl alcohol, 2-ethoxyethanol,acetic acid, 2-aminopyridine, ethylene glycol monomethyl ether,toluene-2,4-diisocyanate, nitromethane, acetonitrile, and the like.Although organic vapor sensors are mentioned as one particular type ofoptical analyte sensors according to the present disclosure, other typesof optical analyte sensors that may be employed include those thatrespond to organic vapors, reactive gases, such as acidic (for example,SO₂, Cl₂, HCl, ClO2, HCN, HF, H₂S and oxides of nitrogen) and basicgases (for example, ammonia, methylamine), and other gases such ascyanogen chloride and formaldehyde.

An exemplary filter system according to the present disclosure isillustrated in FIG. 1, which shows schematically a powered air purifyingrespirator (PAPR) 1. The PAPR 1 includes a head top, such as a hood 12,a turbo unit 14, a breathing tube 13 and a belt 15. The hood 12 isconfigured to be worn over the head of a user 11 and to at leastpartially enclose the user's head to form a breathing zone 17, that is,the area around the user's nose and mouth, so that the filtered air isdirected to this breathing zone 17. Although a hood is illustrated inFIG. 1, the hood 12 could be substituted by any other suitable head top,such as a mask, a helmet or a full suit, provided that a closed userenvironment, covering at least the orinasal area of the user's face, todirect air to the user's breathing zone 17, is created. The turbo unit14 may be attached to a belt 15 to enable it to be secured about theuser's torso.

The turbo unit 14 houses a blower system (not shown), which draws theair through the PAPR system using a fan powered by a motor (also notshown). The turbo unit can further include a power source, such as abattery pack 10. The turbo unit 14 supplies air to the hood 12 throughthe breathing tube 13, which is connected between the outlet 18 of theturbo unit 14 and the inlet 19 of the hood 12. The turbo unit 14includes a filter cartridge (shown in FIG. 2) disposed such that thefilter medium contained therein is in the airflow path, preferablydisposed upstream of a fan opening of the blower. In typical embodimentsof the present disclosure, the filter cartridge is removable withrespect to the turbo unit and replaceable. The purpose of providing thefilter cartridge is to remove at least a certain amount of contaminants,such as particles and/or gases and/or vapors from the ambient air beforethe air is delivered to the user 11.

Embodiments of the present disclosure may employ any one or more of avariety of filter media, one suitable category being sorbent media. Thesorbent media will be capable of sorbing vapors of interest expected tobe present under the intended use conditions. The sorbent mediadesirably are sufficiently porous to permit the ready flow of air orother gases therethrough, and may be in the form of a finely-dividedsolid (e.g., powder, beads, flakes, granules or agglomerates) or poroussolid (e.g., an open-celled foam). Preferred sorbent media materialsinclude activated carbon, zeolites, alumina and other metal oxides thatcan remove a vapor of interest by adsorption; clay and other mineralstreated with acidic solutions such as acetic acid or alkaline solutionssuch as aqueous sodium hydroxide; molecular sieves and other zeolites;other inorganic sorbents such as silica; and organic sorbents includinghypercrosslinked systems, such as the highly crosslinked styrenicpolymers known as “Styrosorbs” (as described for example in V. A.Davankov and P. Tsyurupa, Pure and Appl. Chem., vol. 61, pp. 1881-89(1989) and in L. D. Belyakova, T. I. Schevchenko, V. A. Davankov and M.P. Tsyurupa, Adv. in Colloid and Interface Sci. vol. 25, pp. 249-66,(1986)).

Activated carbons, zeolites, and alumina are examples of preferredsorbent media. Mixtures or layers of sorbent media that can be employed,e.g., to absorb mixtures of vapors or other analytes of interest. If ina finely divided form, the sorbent particle size can vary a great dealand usually will be chosen based in part on the intended serviceconditions. As a general guide, finely-divided sorbent media particlesmay vary in size from about 4 to about 3000 micrometers averagediameter, e.g., from about 30 to about 1500 micrometers averagediameter. Mixtures of sorbent media particles having different sizeranges can also be employed, (e.g., in a bimodal mixture of sorbentmedia particles or in a multilayer arrangement employing larger sorbentparticles in an upstream layer and smaller sorbent particles in adownstream layer). Sorbent media combined with a suitable binder (e.g.,bonded carbon) or captured on or in a suitable support such as describedin U.S. Pat. No. 3,971,373 (Braun et al.), U.S. Pat. No. 4,208,194(Nelson) and U.S. Pat. No. 4,948,639 (Brooker et al.) and in U.S. PatentApplication Publication No. US 2006/0096911 A1 (Brey et al.) may also beemployed.

FIG. 2 shows a filter cartridge 100, which may be used in turbo units ofPAPRs, such as the turbo unit 14 described in connection with FIG. 1.The filter cartridge 100 includes a housing 120 and a filter medium 122,such as a sorbent material, e.g., activated carbon, disposed within thehousing 120. An optical analyte sensor 128 (described in more detailbelow) is also disposed within the housing 120 in fluid communicationwith the filter medium 122, as explained in more detail below. Thehousing 120 illustrated in FIG. 2 includes a back cover 124 a that has aplurality of openings 125 and a front cover 124 b also having aplurality of openings (not shown). The openings in the front cover 124 band the back cover 124 a may serve as gas inlets and outlets,respectively, permitting ambient air from the external environment toflow into cartridge 100, through the filter medium 122 and then into thefan opening of the blower of a turbo unit, of which the filter cartridge100 is a part of. If desired, the openings in one or both of the covers124 a and 124 b could be sealed until use, using, for example, aremovable cover (not shown) that would be removed before use.

A wall 126 of a housing 120 may include a viewing port, such as atransparent portion 127 (which is transparent for the particularspectral range to which the light source(s) and the detector(s) aretuned), through which the optical analyte sensor 128 may be interrogated(as further explained below). If desired, a removable or replaceableshield or other covering (not shown) may optionally be used to protectthe transparent portion 127 from paint or foam overspray, dust, or otherobscuration. Alternatively, the viewing port may include an opening inthe housing 120. In some exemplary embodiments, the entire wall 126 ofthe housing or the entire housing 120 may be transparent. Opticalanalyte sensor 128 is optically responsive to an analyte, for example,by undergoing a change in at least one of its optical properties (as maybe manifested by a colorimetric change, a change in brightness,intensity of reflected light, etc.) when the filter medium 122 becomesequilibrated with the analyte at the conditions of exposure.

The light entering the transparent portion 127 and optical analytesensor 128 is then reflected back through the transparent portion 127.The cartridge 100 would be removed and replaced with a fresh cartridgewhen a discernible change in at least one of the optical properties ofthe optical analyte sensor 128 (e.g., a change in reflectance spectrumsuch as from green to red, an appearance or disappearance of color suchas from white or black to colored or from colored to white or black, ora change from white to black or from black to white) indicates that thefilter medium 122 underneath the optical analyte sensor 128 has becomeequilibrated with the vapor at the conditions of exposure. In otherwords, the optical analyte sensor may be configured such that theoptical change is indicative of the remaining service life for cartridge100 or the end of its service life. In one embodiment, optical analytesensor 128 could be placed at a predetermined location of the flow pathso as to give warning only at the desired remaining service lifepercentage.

FIG. 3A shows a schematic view of an exemplary optical analyte sensorsuitable for use with some exemplary embodiments of the presentdisclosure. A multilayer optical analyte sensor 32 is disposed between atransparent substrate 33 (which is transparent for the particularspectral range to which the light source(s) and the detector(s) aretuned) and filter medium 38. The exemplary optical analyte sensor 32includes a partially reflective layer 34, detection medium 35 and ananalyte-permeable reflective layer 36. Upon the occurrence of or soonafter equilibration at the applied analyte concentration between atleast a portion of the medium 38 and an analyte of interest, the analytecan pass through the analyte-permeable reflective layer 36, for example,through pores 37 into detection medium 35. Detection medium 35 can beprovided in the form of a layer and it can be made from a suitablematerial or made with a suitable structure so that at least one of itsoptical characteristics (e.g., the layer's optical thickness) changesupon exposure to an analyte of interest. The change can be detected fromthe outside, such as through the substrate 33.

A portion of ambient light represented by ray 39 a passes throughsubstrate 33, is reflected from the partially reflective layer 34 aslight ray 39 b, travels back through substrate 33, and then passesoutside substrate 33. Another portion of ambient light ray 39 a passesthrough substrate 33, partially reflective layer 34 and detection medium35 and is reflected from reflective layer 36 as light ray 39 c. Lightray 39 c travels back through detection layer 35, partially reflectivelayer 34 and substrate 33, and then passes outside substrate 33. If anappropriate initial or changed thickness has been chosen for detectionlayer 35, and provided that layers 34 and 36 are sufficiently flat, thenconstructive or destructive interference will be created by the lightrays similar to rays 39 b and 39 c, and a discernible change in one ormore optical characteristics of optical analyte sensor 32 can bedetected through the partially reflective layer 34.

The optical analyte sensors according to the present disclosure may beattached to a filter housing or other support using a variety oftechniques, including film or bulk adhesives, mechanical inserts,thermal bonding, ultrasonic welding and combinations thereof. Thesubstrate is optional, but when present it may be made from a variety ofmaterials capable of providing a suitably transparent support for thethin-film indicator. The substrate may be rigid (e.g., glass) orflexible (e.g., a plastic film that may be handled in one or more rollprocessing steps). If made of a flexible material such as a suitablytransparent plastic, the substrate desirably has sufficiently low vaporpermeability so that the vapor(s) of interest will not be transmittedinto or out of the detection medium through the partially reflectivelayer. If the substrate is omitted then the partially reflective layershould be sufficiently impermeable to discourage or prevent such vaportransmission. A porous substrate may if desired be placed between thepermeable reflective layer and the sorbent media. For example, vapors ofinterest could be allowed to pass from the sorbent media through thepermeable substrate and reflective layer and thence into the detectionmedium.

The partially reflective and reflective layers may each be made from avariety of materials that provide diffuse or preferably specular lightreflection and which can cooperate when appropriately spaced apart toprovide a readily visibly perceptible indicator appearance change.Suitable partially reflective and reflective layer materials includemetals such as aluminum, chromium, titanium, gold, nickel, silicon,silver, palladium, platinum, titanium and alloys containing such metals;metal oxides such as chrome oxide, titanium oxide and aluminum oxide;and the multilayer optical films (including birefringent multilayeroptical films) described in U.S. Pat. No. 5,699,188 (Gilbert et al.),U.S. Pat. No. 5,882,774 (Jonza et al.) and U.S. Pat. No. 6,049,419(Wheatley et al.), and PCT Published Application No. WO 97/01778(Ouderkirk et al.). The partially reflective and reflective layers maybe the same or different. Metal nanoparticle coatings (e.g., metalnanoparticle inks) may be employed to form the reflective layer, asdescribed in copending U.S. Patent Publication No. 2008/0063874A1 (Rakowet al.).

The partially reflective layer is less reflective than the reflectivelayer and transmits some incident light. The partially reflective layermay, for example, have a physical thickness of about 2 to about 50 nm,light transmission at 500 nm of about 20 to about 80%, and reflectanceat 500 nm of about 80 to about 20%, or any number therebetween. Thepartially reflective layer may itself be impermeable to vapor (and if sodesirably is continuous) and optionally coated on or otherwise adjacentto a suitable substrate. The partially reflective layer may also bepermeable to vapor (and if so may, for example, be discontinuous orsemicontinuous) and coated on or otherwise adjacent to a suitablyvapor-impermeable substrate. The face of the partially reflective layeradjacent the detection layer desirably is flat to within about ±10 nm.

The reflective layer may, for example, have a physical thickness ofabout 1 to about 500 nm, light transmission at 500 nm of about 0 toabout 80%, and reflectance at 500 nm of about 100 to about 20%. Thereflective layer preferably is porous, patterned, discontinuous,semicontinuous or otherwise sufficiently permeable so that vapor canpass from the sorbent media through the reflective layer into thedetection medium. The desired pores or discontinuities may be achievedthrough suitable deposition techniques or through appropriatepost-deposition processing such as selective etching, reactive ionetching or patterned laser ablation. The reflective layer may also beformed by depositing a vapor-permeable metal nanoparticle layer asdescribed in the above-mentioned U.S. Patent Publication No.2008/0063874A1 to form a vapor-permeable layer of packed nanoparticles,with pores being provided by interstices between the nanoparticles.

The detection medium mixture may be homogeneous or heterogeneous, andmay, for example, be made from a mixture of inorganic components, amixture of organic components, or a mixture of inorganic and organiccomponents. Detection media made from a mixture of components mayprovide improved detection of groups of analytes. The detection mediumdesirably has a range of pore sizes or a surface area selected toprovide vapor sorption characteristics like those of the sorbent media.Suitable porosity can be obtained by using porous materials such asfoams made from high internal phase emulsions, such as those describedin U.S. Pat. No. 6,573,305 B1 (Thunhorst et al.). Porosity may also beobtained via carbon dioxide foaming to create a microporous material(see “Macromolecules”, 2001, vol. 34, pp. 8792-8801), or by nanophaseseparation of polymer blends (see “Science”, 1999, vol. 283, p. 520). Ingeneral, the pore diameters preferably are smaller than the peakwavelength of the desired indicator coloration. Nano-sized pores arepreferred, e.g., with average pore sizes of about 0.5 to about 20 nm,0.5 to about 10 nm, or 0.5 to about 5 nm.

Representative inorganic detection medium materials include poroussilica, metal oxides, metal nitrides, metal oxynitrides and otherinorganic materials that can be formed into transparent and porouslayers of appropriate thickness for producing color or a colorimetricchange by optical interference. For example, the inorganic detectionmedium materials may be silicon oxides, silicon nitrides, siliconoxynitrides, aluminum oxides, titanium oxides, titanium nitride,titanium oxynitride, tin oxides, zirconium oxides, zeolites orcombinations thereof. Porous silica is an especially desirable inorganicdetection medium material due to its robustness and compatibility withwet etching treatments.

Porous silicas may be prepared, for example, using a sol-gel processingroute and made with or without an organic template. Exemplary organictemplates include surfactants, e.g., anionic or nonionic surfactantssuch as alkyltrimethylammonium salts, poly(ethyleneoxide-co-propyleneoxide) block copolymers and other surfactants or polymers that will beapparent to persons having ordinary skill in the art. The sol-gelmixture may be converted to a silicate and the organic template may beremoved to leave a network of micropores within the silica.Representative porous silica materials are described in Ogawa et al.,Chem. Commun. pp. 1149-1150 (1996), in Kresge et al., Nature, Vol. 359,pp. 710-712 (1992), in Jia et al., Chemistry Letters, Vol. 33(2), pp.202-203 (2004) and in U.S. Pat. No. 5,858,457 (Brinker et al.). Avariety of organic molecules may also be employed as organic templates.For example, sugars such as glucose and mannose may be used as organictemplates to generate porous silicates, see Wei et al, Adv. Mater. 1998,Vol. 10, p. 313 (1998). Organo-substituted siloxanes ororgano-bis-siloxanes may be included in the sol-gel composition torender the micropores more hydrophobic and limit sorption of watervapor. Plasma chemical vapor deposition may also be employed to generateporous inorganic detection materials. This methodology generallyinvolves forming an analyte detection layer by forming a plasma fromgaseous precursors, depositing the plasma on a substrate to form anamorphous random covalent network layer, and then heating the amorphouscovalent network layer to form a microporous amorphous random covalentnetwork layer. Examples of such materials are described in U.S. Pat. No.6,312,793 (Grill et al.) and U.S. Patent Publication No. 2007/0141580A1(Moses et al.).

Representative organic detection medium materials include polymers,copolymers (including block copolymers) and mixtures thereof prepared orpreparable from classes of monomers including hydrophobic acrylates andmethacrylates, difunctional monomers, vinyl monomers, hydrocarbonmonomers (olefins), silane monomers, fluorinated monomers, hydroxylatedmonomers, acrylamides, anhydrides, aldehyde-functionalized monomers,amine- or amine salt-functionalized monomers, acid-functionalizedmonomers, epoxide-functionalized monomers and mixtures or combinationsthereof. The above-mentioned U.S. Patent Application Publication No. US2004/0184948 A1 contains an extensive list of such monomers andreference is made thereto for further details. The above-mentionedpolymers having intrinsic microporosity (PIMs) provide particularlydesirable detection media. PIMs typically are non-network polymers thatform microporous solids. Due to their typically highly rigid andcontorted molecular structures, PIMs are unable to fill spaceefficiently, thus providing the disclosed microporous structure.Suitable PIMs include, but are not limited to, polymers disclosed in“Polymers of intrinsic microporosity (PIMs): robust,solution-processable, organic microporous materials,” Budd et al., Chem.Commun., 2004, pp. 230-231. Additional PIMs are disclosed in Budd etal., J. Mater. Chem., 2005, 15, pp. 1977-1986, in McKeown et al., Chem.Eur. J. 2005, 11, No. 9, 2610-2620 and in Published PCT application No.WO 2005/012397 A2 (McKeown et al.).

One or more polymers within an organic detection medium may be at leastpartially crosslinked. Crosslinking may be desirable in some embodimentsbecause it can increase mechanical stability and sensitivity to certainanalytes. Crosslinking can be achieved by incorporating one or moremultifunctional monomers into the detection medium, by subjecting thedetection medium to, e.g., electron beam or gamma ray treatment, byadding or forming coordination compounds or ionic compounds in thedetection medium, or by forming hydrogen bonds in the detection medium.In one exemplary embodiment, crosslinking is carried out in the presenceof a porogen which may be subsequently extracted from the crosslinkedsystem to yield a porous detection medium. Suitable porogens include,but are not limited to, inert organic molecules, such as normal alkanes(e.g., decane) or aromatics (e.g., benzene or toluene). Othercrosslinked polymers include the above-mentioned highly crosslinkedstyrenic polymers.

If desired, the detection medium material may be treated to modify itssurface properties or adsorption characteristics. A variety of suchtreatments may be employed, e.g., by exposing the micropores of aninorganic detection medium to a suitable organosilane compound. Thedetection medium may also or instead be treated with a suitable adhesionpromoting material (e.g., a tie layer made of titanium or anothersuitable metal) to promote adhesion between the partially reflective orreflective layer and the detection medium. Such treatments may also beapplied to the partially reflective or reflective layers to promoteadhesion to the detection medium.

For many applications, the detection medium desirably is hydrophobic.This will reduce the chance that water vapor (or liquid water) willcause a change in the detection medium optical thickness and interferewith the detection of an analyte, for example, the detection of organicsolvent vapors. The detection medium may be made from a single layer orfrom two or more sublayers. The sublayers may have a variety ofconfigurations. For example, they may be stacked or arranged side byside. The sublayers may also be made from different materials selectedto absorb different vapors of interest.

Another exemplary embodiment of an optical analyte sensor suitable foruse in embodiments of the present disclosure is shown in FIG. 3B. Asshown in FIG. 3B, the optical analyte sensor 40 may include one or morefirst regions 42 that exhibit a first response to an analyte of interestand one or more second regions 44 that exhibit a second, different,response to an analyte of interest. Such optical analyte sensors areherein referred to as patterned optical analyte sensors. In theillustrated embodiment, the optical analyte sensor 40 has a multilayerconstruction, which includes a detection medium 48, a semi-reflectivelayer 50, and a reflective layer 52. Detection medium 48 can be providedin the form of a layer and it can be made from a suitable material ormade with a suitable structure so that at least one of its opticalcharacteristics (e.g., the layer's optical thickness) changes uponexposure to an analyte of interest. The change can be detected from theoutside, such as through a substrate 46, which may comprise a wall of ahousing.

The change is expected to be different in the first and second regions42 and 44. Any detectable difference that is discerned by a detectoremployed is within the scope of the present disclosure. For example, inresponse to being exposed to an analyte of interest, different regionsof an optical analyte sensor according to the present disclosure mayexperience different magnitudes of spectral shifts, such as differentpeak wavelength shifts, different intensities of reflected light, orboth. Some detectors are capable detecting a difference in a color shiftof as little as 1 nm. The semi-reflective layer 50 generally notpermeated by the vapor. The reflective layer 52 is generally permeableto the chemical and is in fluid communication with the filter medium 60such that the analyte of interest can pass through the reflective layer52 into the detection medium 48 and can change at least one opticalcharacteristic of the detection medium, such as its optical thickness,sufficiently to cause a change that can be detected by an optical readeraccording to the present disclosure, upon interrogation. An adhesive 53may be used to secure the sensor 40 to an inner surface of a housingwall 46.

One way of producing an optical analyte sensor that includes one or morefirst regions that exhibit a first response to an analyte of interestand one or more second regions that exhibit a second, different,response to an analyte of interest, is by disposing an occluding layer54 over a portion of a surface of the optical analyte sensor 40 that isin fluid communication with the filter medium 60. In the illustratedembodiment, occluding layers 54 are disposed on opposing sides of thesecond region 44, which region 44 changes color in response to exposureto one or more analytes of interest. The occluding layer 54 may bebonded to the reflective layer 52 at an interface 56 directly or via oneor more intermediate layers. The interface 56 may be an adhesive layer.

Without an inert occluding layer 54 bonded to the optical analyte sensorbody 58, the sensor would normally undergo a similar change in at leastone of its optical characteristics over the regions 42 and 44. However,when the occluding layer 54 is disposed over the body 58, the sensor isnot expected to undergo a change in at least one of its opticalcharacteristics over the regions corresponding to the area masked by theoccluding layer 54, such as the regions 42. However, the sensor isexpected to undergo a change in at least one of its opticalcharacteristics over the regions corresponding to the area not masked bythe occluding layer 54, such as the regions 44. However, because in someembodiments the regions 42 and 44 may be adjacent or integral, theabove-referenced change may be a progressive one. The boundary betweenregions 42 and 44 may be abrupt or gradual. In other exemplaryembodiments, the regions may not be adjacent. The occluding layer(s) asdescribed above may be applied to sensors to produce a variety ofdifferent visual patterns useful for interrogation according to thepresent disclosure.

In one embodiment, adhesives, such as pressure-sensitive adhesives maybe used to form occluding layers. Polyisobutylene (PIB) adhesives areuseful materials for these layers based especially on their high purity.One example of such a commercially available acrylic-based pressuresensitive adhesive transfer tape useful in embodiments of the presentdisclosure is 3M's adhesive transfer tape known under the trade name VLO6690. Other pressure-sensitive adhesives useful for film body maskingmay include acrylic-based adhesives. In one embodiment, thepressure-sensitive adhesives may be applied to the sensor in the form ofpressure-sensitive tapes, which may further include a liner and/or orbacking. In this implementation, the liner and/or backing often providesan additional barrier to permeation of vapors into the sensor. Hot melt,solution-free, adhesives can also be applied as masking materials.Polymeric materials can also be used as occluding layers to mask regionsof the sensor, such as water-soluble polymers or epoxy materials, whichmay be UV or thermally curable. Waxes, resins or inorganic materialsalso may be used for the occluding layer.

Additionally or alternatively, any other layer or one of a set ofsublayers of an exemplary optical analyte sensor may be discontinuous orpatterned to achieve one or more first regions that exhibit a firstresponse to an analyte of interest and one or more second regions thatexhibit a second, different, response to an analyte of interest. Layeror sublayer patterns may also be formed by providing one or moreportions that are reactive to a particular analyte and one or moreportions that are non-reactive to the same analyte. A pattern ofreactive material may also be deposited on a larger non-reactivesublayer, e.g., by making the patterned layer sufficiently thin so thatno difference in optical thickness is apparent until an analyte isabsorbed. The thickness of the detection layer may also be patterned,e.g., as described in U.S. Pat. No. 6,010,751 (Shaw et al.). This canpermit a pattern to disappear (for example when a thinner portion swellsto the same thickness as a thicker portion) or to appear (for example,when a portion shrinks to a lesser thickness than an adjacent portion).If desired, discontinuities may be formed in the reflective layer in thepattern of a desired shape or form. This can cause a discernible patternto emerge or disappear upon exposure to the analyte of interest. In somecases, it may be easier to detect the contrasting optical properties ofsuch a pattern than to detect an optical change in the overall indicatorfilm.

The disclosed devices may include additional layers or elements ifdesired. For example, a porous layer of sorbent-loaded composite (e.g.,a web of activated carbon particles ensconced in a matrix of fibrillatedPTFE such as is described in the above-mentioned U.S. Pat. No.4,208,194) may be placed between the reflective layer and the sorbentmedia, to homogenize vapors permeating into the indicator or otherwisemoderate the indicator response to conditions in the sorbent media.

Various constructions and materials suitable for use in optical analytesensors according to the present disclosure are described, for example,in U.S. Application Publication No. 2008/0063874A1 entitled “PermeableNanoparticle Reflector,” U.S. application Ser. No. 12/604,565 entitled“Patterned Chemical Sensor Having Inert Occluding Layer,” and U.S. Pat.No. 7,449,146, entitled “Colorimetric Sensor.” Commonly owned U.S.Application Publication No. 2008/0063575A1 and U.S. application Ser. No.12/604,565 entitled “Patterned Chemical Sensor Having Inert OccludingLayer,” describe using visibly discernible changes in the appearance ofan indicator to provide a user of an organic vapor sorbent protectivedevice with information indicative of the remaining service life or ofthe end of service life for a cartridge. In that application, theappearance changes in indicator could be visibly monitored under ambientlighting.

Embodiments of the present disclosure, however, include or are directedto optical readers configured to detect a change in at least one of theoptical characteristics of an optical analyte sensor in response to atarget analyte. The present disclosure thus is capable of providing anaccurate end of service life indication without relying on a user'svisual check of the color changing sensor. Visual check of the film bythe user can provide an end of service life indication for someanalytes, but in other cases, especially under conditions of low analyteconcentration, some volatile organic compounds of interest do notproduce a noticeable color change. On the other hand, some analytesproduce such a massive color shift that they force the optical analytesensor to return to its original color, which is sometimes referred toas the wrap around effect. For example, a sensor could change color fromgreen to red to green again. Thus, some benefits of the presentdisclosure include increasing the range of volatile organic vapors thatcan be detected and preventing wrap around effects from affecting theend of service life indication.

FIG. 4 shows an exemplary optical reader 200 according to the presentdisclosure. The optical reader 200 includes at least one light source(here, 212 and 214) and at least one detector 220. One or more lightsources (e.g., 212 and 214) and one or more detectors 220 can be mountedon the same support 250. The optical reader 200 can be configured to beattached to a housing of a filter system according to the presentdisclosure, including an optical analyte sensor 230, such that at leasta portion of light 212 a, 214 a emitted by at least one light source212, 214 is reflected from the optical analyte sensor 230 and capturedby the at least one detector 220.

One or more light sources (e.g., 212 and 214) may include any of avariety of light sources. For example, light-emitting diodes (LEDs) canbe used. In certain embodiments, one or more light sources may includeone or more relatively broadband light sources (e.g., white lightsources). In other embodiments, light sources may include one or morenarrowband light sources (e.g., LEDs) that emit light in a particular(e.g., relatively narrow) wavelength range with a peak at a particularwavelength within that range. In various embodiments, such narrowbandlight sources may be characterized by a half-power bandwidth of at mostabout 50 nm, at most about 40 nm, or at most about 25 nm. Exemplary LEDsthat may be used include those available from Optek, Carrollton, Tex.,under the designation OVLBx4C7, and surface mount LEDs such as the LST676, LA T676, LO T676, LY T676 series from Osram.

A detector (e.g., 220) suitable for use in exemplary embodiments of thepresent disclosure may include any of a variety of devices capable ofmeasuring the amount of light incident thereon, including for examplephotodetectors such as photomultiplier tube, a photovoltaic cell, aphotodiode, a phototransistor, a charge coupled device, and the like. Asuitable detector may serve to provide a signal (e.g., voltage, current,etc.) that is related to the amount of light detected (e.g., to theintensity or strength of the reflected light received from the opticalanalyte sensor 230) and that can be further processed as described laterherein. In some embodiments one or more detectors may detect light of aparticular (e.g., relatively narrow) wavelength range. In otherembodiments, one or more detectors may include a broadband detector thatcan detect light over relatively wide range of wavelengths. In variousembodiments, such broadband detectors may be able to detect light over awavelength range of at least about 150 nm wide, 250 nm wide, or 500 nmwide. Exemplary detectors that can be used include photodiodes availablefrom OSRAM, Regensburg, Germany, under the designation SFH 2430.

As illustrated in FIG. 4, multiple light sources may be used as a partof the optical reader 200. In the illustrated exemplary embodiment,first and second light sources 212 and 214 each may be characterized byfirst and second spectral (or wavelength) ranges and first and secondpeak wavelengths. The first spectral range may be different from thefirst spectral range and the first and second light sources can emitlight with different peak wavelengths. In such a design, the differentlight sources 212 and 214 may be mounted next to a common detector 220(an exemplary design involving a detector 220 disposed between two lightsources 212 and 214 is shown in FIG. 4).

First and second light sources 212 and 214 may be chosen such that theirspectra are characterized by different wavelength ranges A and B anddifferent peak wavelengths corresponding to peaks 2001 and 2002(illustrated in FIG. 5A), respectively. In such embodiments, a single(e.g., broadband) photodetector may be used as the detector 220. Themonitoring of light reflected from the optical analyte sensor inmultiple wavelength ranges may provide significant advantages. Thevarious details and principles of such detection are set forth, forexample, in a commonly owned U.S. Provisional Application No. 61/164,496(Hulteen et al.). In particular embodiments, wavelength range A may bechosen to fall at or near the maximum of a peak (e.g., peak 2000 shownin FIG. 5A) in the reflection spectrum of the optical analyte sensor inthe absence of a target analyte. Wavelength range B may be at leastsomewhat removed from wavelength range A, and in some embodiments may beat or near a valley minimum (e.g., valley minimum 2003 shown in FIG. 5A)in the reflection spectrum of an optical analyte sensor in the absenceof the target analyte. In particular embodiments, wavelength B falls ator near valley minimum that is immediately adjacent to a peak of whichwavelength λ is monitored. FIG. 5A illustrates this concept by showingemission bands of two exemplary light sources superimposed with areflection spectrum of an exemplary optical analyte sensor using a PIMfilm. Photodetector sensitivity to wavelength of incident light is shownin FIG. 5B. As the spectrum shifts towards right upon adsorption of thetarget analyte, the photodetector response for the green light sourcegradually starts declining while the response for the red light sourcestarts increasing. Using a ratio of the responses of the first andsecond light sources is desirable, as it can help reduce the impact offluctuations in the intensity of light delivered by a light source.

The specific wavelength ranges chosen may depend upon the properties ofthe particular optical analyte sensor that is used, the particularanalyte(s) that is desired to be monitored, etc. In various embodiments,wavelength range A and wavelength range B are chosen such that theircenterpoints are at least 20, at least 40, or at least 60 nanometersapart. In further specific embodiments, wavelength range A andwavelength range B are chosen such that their centerpoints are at most140, at most 120, or at most 100 nm apart. In various embodiments, thecenter of the first wavelength range may be within about 10 nm, 20 nm,or 40 nm of a peak maximum, and the center of the second wavelengthrange may be within about 10 nm, 20 nm, or 40 nm of a valley minimum. Insome embodiments, optical interrogation may be performed whereinwavelength range A is centered around approximately 520 nm, and whereinwavelength range B is centered around approximately 640 nm. In otherembodiments, optical interrogation may be performed wherein wavelengthrange A is centered around approximately 591 nm, and wherein wavelengthrange B is centered around approximately 606 nm. As mentioned,interrogation in wavelength ranges A and B may be achieved, e.g., by useof narrowband light sources such as LEDs and the like. In otherembodiments, broad-band light sources could be filtered using narrowbandor band pass filters to tune the wavelength range to a desired spectralregion. In some exemplary embodiments, one or more wavelength ranges canbe in the UV or near infra-read regions of the spectrum. PIM opticalanalyte sensors, for example, exhibit peaks and valleys in those regionsand, therefore, one may provide sensor/reader combinations configured tooperate in those regions of the spectrum. If desired, additional opticalinterrogation may be performed at other wavelength ranges. Suchadditional ranges may be between ranges A and B, overlapping with rangesA and B, or outside ranges A and B. Such additional opticalinterrogation ranges (which may be provided, e.g., by the use ofadditional light sources) may provide enhanced resolution, dynamicrange, precision, etc.

In such configurations, a signal from a detector indicative of theamount of light detected in wavelength range A can be compared (e.g.,ratioed by a microprocessor), to a signal from a detector indicative ofthe amount of light detected in wavelength range B. Suchcomparison/ratioing may provide significant advantages. For example, itmay allow the confirmation that a new or replacement optical analytesensor is in operating condition (e.g., has not been prematurely exposedto analyte, damaged, out of alignment, etc.), as further describedbelow. Thus in some embodiments, methods disclosed herein include thestep of obtaining an initial compared signal and determining whether theinitial compared signal is in an acceptable range. Use of compared(e.g., ratioed) signals may also enhance the dynamic range of theoptical reader. In the context of the methods disclosed herein, thecomparing of first and second signals (e.g., signals indicative of anamount of light detected in a first wavelength range and a secondwavelength range) can include the comparing of averaged signals (e.g.,the obtaining of multiple first signals and averaging them and theobtaining of multiple second signals and averaging them, and comparingthe averaged first signal with an averaged second signal), as well asthe comparing of an individual first signal with an individual secondsignal.

FIG. 6 shows schematically another exemplary embodiment of an opticalreader 300 according to the present disclosure. The optical reader 300includes two light sources 312 and 314 and two detectors 322 and 324.One or more light sources and one or more detectors can be mounted onthe same support 350. Such an optical reader also can be configured tobe attached to the housing of a filter system according to the presentdisclosure, including a optical analyte sensor, such that at least aportion of light emitted by at least one light source 312, 314 isreflected from the optical analyte sensor 330 and captured by thedetectors 322 and 324. In this exemplary embodiment, light sources 312and 314 each may emit light in a different wavelength range with adifferent peak wavelength than that emitted by the other light source.Each light source 312 and 314 can be used in combination with aphotodetector 322 and 324, respectively, designed to detect light in theparticular wavelength range emitted by the corresponding light source.

FIG. 7A shows an exemplary embodiment of an optical reader 400 utilizingone or more broadband light sources 410. The broadband light source 410can be or include one or more broadband light sources, such as whiteLEDs. When more than one broadband light source is used, at least two ofthe light sources can be configured to have different spectral rangesand/or profiles, as described above in connection with exemplaryembodiments utilizing narrowband light sources. The emission spectra ofone or more of the broadband light sources can be tailored simply bypurchasing a commercially available light source with a desired spectrumor by placing one or more spectral filters over one or more of thebroadband light sources, such as the spectral filters known to those ofordinary skill in the art. A suitable spectral filter may include anoptical coating over a transparent substrate. Alternatively, two or morenarrow band light sources characterized by different wavelength rangesas well as different peak wavelengths may be used together to simulate abroad band light source. For example, light sources characterized bywavelength ranges and peak wavelengths covering different primary colorregions could be used in combination to simulate a while light source.Particularly, one or more of red, green and blue LEDs can be used incombination.

Such exemplary embodiments can also include a color-sensing detector420. Such a detector allows a more direct measurement of the color ofthe optical analyte sensor, rather than simply a reflectance within aparticular spectral range of illumination. A color-sensing detector canbe implemented as a multi-pixel photodetector array that includes two ormore (preferably, three or more) sets of photodetectors that aresensitive to only two or more (preferably, three or more) differentrelatively narrow wavelength ranges. In one exemplary embodiment, such acolor-sensing photodetector may include banks of red, green, blue andwhite photodetectors, such as photodiodes. Another exemplarycolor-sensing detector may include an array of the same or similarphotodetectors overlaid with a spectral filter to achieve a similarresult. One example of spectral filter suitable for such exemplaryembodiments is a filter having areas with different spectraltransmissions, such as a tiled spectral filter 424 disposed over adetector array 422, as shown in FIG. 7B. The spectral filter 424includes areas (tiles) characterized by different spectraltransmissions. For example, one or more tiles 424 a may be characterizedby high transmission of red light, one or more times 424 b may becharacterized by high transmission of blue light, and one or more tiles424 c may be characterized by high transmission of green light. Oneexample of such a spectral filter is a Bayer filter.

Referring further to FIG. 7A, an optical analyte sensor 430 isilluminated by the light source(s) 410 and the reflected signal isdetected by the detector 420. A programmable logic device such as amicroprocessor may then decompose the detector optical response intoprimary colors, such as R, G, B. The decomposed responses can beprocessed to infer any relevant information (such as whether a changehas occurred in at least one of the optical characteristics of theoptical analyte sensor 430, whether the reader 400 is in alignment withthe sensor 430, etc.) using standard algorithms. In yet other exemplaryembodiments, a broadband light source can be used in combination withone or more narrowband detectors. Alternatively, interrogation at agiven predetermined wavelength range may achieved by the use of anarrowband light source in combination with a narrowband or broadbanddetector.

The use of multiple or broadband light sources and/or multiple orbroadband photodetectors may allow enhanced operation of the opticalreader. For example, such designs may allow the detection of a widerrange of detectable analytes, may allow a wider concentration range ofanalyte to be detected, may allow more precise quantitation of theconcentration of analyte, may negate the need to calibrate the opticalreader each time that a new or replacement optical analyte sensor isinstalled, and so on. Thus in some embodiments, performance of themethods described herein does not require that the sensing element isexposed to a calibration gas containing a known non-zero concentrationof analyte, prior to the monitoring of an atmosphere potentiallycontaining the analyte. Further, an advantage of using colormeasurements as described above is that it does not require tailoringthe optical analyte sensor for any particular predetermined spectralregion.

FIGS. 8A and 8B show opposing first and second sides 500 a and 500 b ofanother exemplary embodiment of an optical reader 500 according to thepresent disclosure for interrogating an optical analyte sensor accordingto the present disclosure. The optical reader 500 includes first andsecond light sources 512 and 514 and a detector 520. The first lightsource is characterized by a first spectral profile, and a second lightsource is characterized by a second spectral profile. For example, thefirst light source may be characterized by a first peak wavelength and afirst wavelength range, and a second light source may be characterizedby a second peak wavelength and a second wavelength range. In typicalexemplary embodiments, the first spectral profile is different from thesecond spectral profile. For example, the first and second peakwavelengths and/or the first and second wavelength bands may bedifferent. In this exemplary embodiment, first and second light sources512 and 514 and a detector 520 can be mounted on the same support 550,such as a printed circuit board. The optical reader may further includea programmable logic device 540, which is preferably also mounted on thesupport 550.

The optical reader 500 may further include a battery 530, an alertingdevice, such as one or more light sources 516 and 518, and an actuator560, all of which are shown in FIG. 8B. A user may trigger the actuator560 to initiate the interrogation of an optical analyte sensor by theoptical reader 500. The optical reader 500 may be connected to anotherdevice, such as a computer by a wireless interface or by a serialinterface. Thus, the optical reader may communicate various informationto a database or a display, such as data obtained by the optical readerfrom interrogating an optical analyte sensor according to the presentdisclosure. Typically, a serial interface is used during testing,qualification, and/or calibration of the optical reader.

Preferably, first and second light sources 512 and 514 are disposed onone side of the support 550, while the detector 520 is disposed on anopposing side of the support 550. In this exemplary embodiment, thesupport has an opening 520 a so that light returning from the opticalanalyte sensor could reach the detector 520. Light sources can bemounted on (e.g., attached to) a printed circuit board at an anglerelative to printed circuit board, so as to establish the desired anglebetween light source(s), detector and optical analyte sensor. If one ormore light sources are light-emitting diodes, they may be electricallyconnected to printed circuit board via any known mounting method.Through-hole methods may be better able to establish the desired angle,although surface mount methods may be used if desired. If desired, oneor more positioning devices (e.g., holders, collars, etc.) may be usedto position one or more light sources on the printed circuit board atthe desired angle.

One or more of the above-referenced components of the optical reader maybe disposed in an interior of a housing 580. Preferably, at least firstand second light sources 512 and 514, the detector 520, and the support550 are disposed in the interior of the housing. However, any number ofcomponents of the optical sensor 500 may be enclosed in the housing 580,and, in some cases, all of its components. Optical reader housingsaccording to the present disclosure may be constructed with materialstransparent for light of the visible spectrum, such as glass ortransparent plastics, e.g., polycarbonate, nylon, polystyrene.Alternatively, an optical reader housing can be made from an opaquematerial with a transparent portion disposed over the detector and oneor more light sources, such that the optical reader would be capable ofirradiating and receiving light from an optical analyte sensor it isconfigured to read. The shape of the housing may be any shape suitablefor a filter system it is intended to be used with. In yet otherexemplary embodiments, the housing may be or include a portion opaque tolight of visible spectrum but transparent to light of other spectralregions, such as one or more where infrared or near infrared lightsources and detectors are used.

In typical embodiments of the present disclosure the housing includes aregistration feature 582 (here, a slot) configured to align the opticalreader 500 with a optical analyte sensor, as is explained in detailbelow. The size and shape of the registration feature may vary dependingon the application. In some exemplary embodiments, more than one of thesame or different registration features may be included in an opticalreader. The optical reader can be configured to be attached to thehousing of a filter system according to the present disclosure includingan optical analyte sensor, such that at least a portion of light emittedby at least one light source 512, 514 is reflected from an opticalanalyte sensor it is designed to interrogate and captured by thedetector 520. The construction of the exemplary embodiment illustratedin FIGS. 8A and 8B enables one to make use of surface mount optics toarrive at a thin and small form factor reader capable of being held onor at the surface of a filter system such as a filter cartridge as shownand described below. In typical embodiments, the optical reader is verycompact and low profile. For example, an optical reader such as thereader shown in FIGS. 8A and 8B may have a typical length L of 20 mm, 60mm, 100 mm, 150 mm, or any number between any of these values. A typicalwidth W of such an optical reader may be 10 mm, 30 mm, 40 mm, 70 mm, orany number between any of these values. A typical weight of opticalreaders according to the present disclosure may be 5 g, 8 g, 50 g, 100g, or any number between any of these values.

FIG. 9A shows an exemplary optical reader 80 according to the presentdisclosure, which is configured to interrogate a patterned opticalanalyte sensor 70 having a first region 72 that exhibit a first responseto an analyte of interest and a second region 74 that exhibit a second,different, response to an analyte of interest. In some exemplaryembodiments, the first response is greater than the second response.Such exemplary patterned sensors are described, for example, inreference to FIG. 3B of the present disclosure. In this particularexemplary embodiment, the first region 72 is configured to serve as areference, i.e., it does not exhibit a significant (preferably,detectable) response to an analyte of interest. In the second region 74,however, exhibits a change in at least one of the opticalcharacteristics of the optical analyte sensor 70 in response to ananalyte of interest.

The optical reader 80 includes at least one light source 82 and at leastone detector 84. The optical reader 80 is configured such that, when itdisposed in proper alignment to interrogate the optical analyte sensor70, it can be considered to interrogate the optical analyte sensor 70 inboth the first region 72 and the second region 74. In one embodiment,the light source 82 and the detector 84 each have a projection of lightarea 82 b and detection area 84 b, respectively, as illustrated in FIG.9A. The areas 82 b and 84 b are determined by the solid angle of light82 a emitted by the light source 82 and the solid angle of detection 84a, usually set or designed by the manufacturer. By choosing theopto-electronics with suitable solid angles and by carefully placingthem on a support 85, such as a PCB, one can design an optical readerwith interrogation capabilities illustrated in FIG. 9A. If the lightsource 82 and the detector 84 are at the border 70 a between the firstand second regions 72 and 74, by varying the separation distance betweenthe reader and the sensor, and the distance between the light source andthe detector, one can increase or decrease the surface area on thepatterned film that the light source illuminates and that the detectorcaptures light from.

Preferably, a half of the area 82 b, 84 b (which areas may or may notcoincide) would be in the first region 72 of the optical analyte sensor70 and the other half of the area 82 b, 84 b would be in the secondregion 72 of the optical analyte sensor 70. Generally, at least aportion of light emitted by the light source 82 is reflected from thefirst region 72 and captured by the detector 84. Similarly, at least aportion of light emitted by the light source 82 is reflected from thesecond region 72 and captured by the detector 84. Thus, the light 84 areceived by the detector 84 would be the sum of light received from thefirst and second regions 72 and 74. For an optical analyte sensor thathas not been exposed to an analyte of interest, the detector response toboth the first and second regions 72 and 74 would be similar. However,upon exposure, as at least one of the regions 72 and 74 begins toexperience a change in at least one of its optical characteristics,detector reading will change accordingly.

Another exemplary optical reader according to the present disclosure isshown in FIG. 9B, which shows an optical reader 90, configured tointerrogate a patterned optical analyte sensor 70 having a first region72 that exhibit a first response to an analyte of interest and a secondregion 74 that exhibit a second, different, response to an analyte ofinterest. The change in at least one of the optical characteristics ofthe optical analyte sensor 70 in response to an analyte of interest maybe detected by one or more detectors 92 a-92 d.

The optical reader 90 includes a first assembly 192 and a secondassembly 191. With respect to the illustrated embodiment, the firstassembly may be referred to as the sensing assembly and the secondassembly may be referred to as the reference assembly. The referenceassembly includes one or more (here, two) light sources 93, 95 and oneor more (here, one) detectors 91. The optical reader 90 is configuredsuch that, when it disposed in proper alignment to interrogate theoptical analyte sensor 70, at least a portion of light emitted by atleast one light source 93, 95 is reflected from the first region 72 ofthe optical analyte sensor 70 and captured by the at least one detector91. The sensing assembly 192 includes one or more blocks of one or morelight sources and one or more detectors. In this exemplary embodiment,the sensing assembly 192 includes four blocks, each block including twolight sources 94 a-d and 96 a-d and a detector 92 a-d. The opticalreader 90 is configured such that, when it disposed in proper alignmentto interrogate the optical analyte sensor 70, for each block of thesensing assembly 192, at least a portion of light emitted by at leastone light source 94 a-d, 96 a-d is reflected from a particular area(A-D) of the second region 74 of the optical analyte sensor 70 andcaptured by the at least one detector 92 a-d. In particular, at least aportion of light emitted by the first block first and second lightsources 94 a and 96 a reflected from a first area A of the second region74 of the optical analyte sensor 70 is captured by the first blockdetector 92 a; at least a portion of light emitted by the second blockfirst and second light sources 94 b and 96 b reflected from a secondarea B is captured by the second block detector 92 b; at least a portionof light emitted by the third block first and second light sources 94 cand 96 c reflected from a third area C is captured by the third blockdetector 92 c; and at least a portion of light emitted by the fourthblock first and second light sources 94 d and 96 d reflected from afourth area D is captured by the fourth block detector 92 d.

Preferably, the first, second and fourth blocks are positioned over theAreas A, B, C and D of the optical analyte sensor 70, such that there isno overlap between the areas interrogated by the different blocks. Insuch exemplary embodiments, as an analyte of interest propagates througha filter medium that is in fluid communication with an optical analytesensor according to this exemplary embodiment, the regions A, B, C and Dof the second, responsive, region 74 of the optical analyte sensor 70will be sequentially exposed to the analyte and, therefore, sequentiallyundergo a change in at least one optical property. In particular if theoptical change is experienced first by the area A, then B, then C, and,finally, D, then the first, second, third and fourth blocks of thesensing assembly 192 will detect the sequential change in the sameorder. Thus, the present exemplary embodiment allows for a multi-stepindicator. For example, one such positioning would provide indication of100%, 75%, 50%, 25%, and 0% remaining service life respectively.

Although four blocks are shown in the sensing assembly and one block isshown in the reference assembly, any other suitable number of blocks maybe used consistently with the present disclosure. Light sources,detectors, optical analyte sensors, and other components and devicessuitable for use in this exemplary embodiment may be any suitablesystem, element or assembly described above or any other suitablesystem, element or assembly.

Upon interrogation of an optical analyte sensor using methods anddevices disclosed herein, a signal may be obtained that is related tothe presence and/or concentration of an analyte of interest. In someembodiments, the signal generated by the at least one photodetector ofthe optical reader is an electrical signal, e.g., in the form of avoltage or current. Such a signal can then be manipulated, processed,etc. Optical readers according to the present disclosure may include oneor more analog to digital converters that can provide the signal in adigital form for ease of processing by a programmable logic device, suchas a microcontroller, microprocessor or a field programmable gate array,in the event that the signal is initially in an analog form. In case ofmultiple detectors, a separate signal may be provided by each detector.

The signals received from the one or more photodetectors can bemathematically manipulated (individually or in combination) according toalgorithms resident in the circuitry of the optical reader (e.g., loadedinto software or firmware) as desired. Thus, the optical reader maycomprise such components, circuitry, etc., as needed to perform suchdesired signal processing, and also as needed to control the lightsource(s) and/or photodetector(s). With reference to the block diagramof FIG. 10, optical readers of the present disclosure may include aprogrammable logic device, such as a microcontroller, microprocessor ora field programmable gate array, 137 that may operate light source(s)131 and operate (and receive signals from) photodetector(s) 132, mayprocess, manipulate, etc., signals received from photodetector(s) 132,may hold various data and parameters in memory, may operate an alertingdevice 136, such as an indicator or a display, and communicate with auser via an interface 139, such as a wireless or serial interface, mayreceive power from (internal or external) power source 134 via powersupply 135, and may carry out other functions as needed.

For example, signals collected from photodetector 132 may be heldresident in memory (e.g., of microprocessor 137) so that thetime-dependent history of the signals may be accessed and consulted.This may be useful, for example, in a case in which (e.g. in thepresence of a certain amount of analyte) a second peak in the opticalanalyte sensor reflectance spectrum shifts sufficiently close to the Awavelength range that a signal is received in the A wavelength rangeresulting from a peak that is similar to that initially received from afirst peak in the absence of analyte. By following the time-dependenthistory of the signals received from photodetector 132 (e.g., the signalin wavelength range A falling, then rising again towards its initialvalue) embodiments of the present disclosure might be able todistinguish such a condition (e.g., perhaps caused by a very largeamount of analyte) from a condition in which a relatively constantreflected light signal is received over the time period of the potentialanalyte exposure. Similar signal processing may be performed when usingcompared (e.g., ratioed) signals.

Other information may be held resident in memory of microprocessor 137to provide enhanced functioning of exemplary embodiments of the presentdisclosure. For example, information regarding one or more predeterminedconditions to which a signal from one or more detectors may be compared(e.g., a predetermined response curve, empirically derived or obtainedvia exposure of a sensing element to known analyte concentrations) maybe provided that relates a signal (e.g., the intensity of light atwavelength range A); or, a compared signal (e.g. the ratio of theintensity of light at wavelength range A to that at wavelength range B),etc., to a concentration of analyte in a monitored environment.Exemplary embodiments can thus function by correlating a compared signalto a predetermined response curve so as to obtain a concentration valuethat is associated with, or representative of, the concentration of ananalyte. A single response curve may be preloaded (e.g., permanently)into the memory of an exemplary embodiment; or, response curves may beuploaded periodically into the memory for use with particular designs ofoptical analyte sensors, particular analytes, and so on. Multipleresponse curves may be used. In the context of the methods disclosedherein, such correlating of a compared signal with a response curveencompasses the correlating of an averaged compared signal (e.g.,resulting from the obtaining of multiple compared signals and averagingthem), as well as the correlating of an individual compared signal.Correlation of signal obtained by the detector with a thresholdmaintained in memory can also allow users to set their own criteria fortriggering a particular response, such as a visual or audibleindication, data logging, etc. In environments with highly toxiccontaminants, for example, a user may want the sensor to respond to verylow concentrations and can set this threshold accordingly. In contrast,a low toxicity contaminant may not require a threshold to be set as low.

In summary, embodiments of the present disclosure, based on the signalsreceived and/or processed as described herein, may produce, via analerting feature, a notification signal that is associated with, e.g.representative of, the presence of an analyte of interest at a specificlocation in the sorbent bed. The notification signal can be communicatedto a user of exemplary embodiments of the present disclosure by analerting feature (for example, by a visual, audio, or tactile signal).In one embodiment, the notification signal can be an actual numericalvalue of the concentration of the analyte. In addition to this, and/orinstead of this, and notification signal can be provided that, while nota numerical value, is associated with such a numerical value. Forexample, embodiments of the present disclosure may provide an auditorysignal (e.g., a beep, chirp, alarm signal), a visual signal, such as oneor more light indicators, and/or a vibrational signal, upon thedetection of the analyte, and/or of the detection of a certain amount ofthe analyte. In some exemplary embodiments, the alerting device may becapable of providing at least one of a visual and audible indication. Inone embodiment, the alerting device includes one or more flashing lightsand/or light indicators of different colors (e.g., green light to showthe optical reader is working and red to indicate a particularcondition).

Some embodiments of the present disclosure may provide nonquantitativeindications, (for example, indicating whether an analyte of interest ispresent, e.g., above a certain concentration). Some embodiments mayprovide semiquantitative and/or quantitative information (e.g., anestimate or indication of the concentration of the analyte). Someembodiments may provide a cumulative indication (that is, an integratedindication that arises from the concentration of analyte in themonitored air over a period of time that may range up to a few hours).This type of indication is useful to relate the progression of acontaminant through the filter system to the user. In some otherembodiments, embodiments of the present disclosure may provide periodicor even “real time” readings. In some embodiments, exemplary embodimentsof the present disclosure may communicate, either in real time orperiodically (e.g. by transmission of datalogged information), suchinformation to a receiving station or a remote device, such as adatabase. For example, exemplary embodiments of the present disclosuremay transmit such information (e.g., by wireless or infraredtransmission) to a computer, workstation, central processing facility,or the like. Wireless interface included on an embodiment of theinvention can provide a seamless and transparent way of communicatingthe real time or periodic status updates of the filter system to a uservia a wireless display or to a supervisor or industrial hygienist.

FIGS. 11A, 11B, 11C and 11D show another exemplary filter system 600according to the present disclosure. This exemplary filter system is afilter cartridge 600, which may be used in turbo units of PAPRs, such asthe turbo unit 14 described in connection with FIG. 1. The filtercartridge 600 includes a housing 620 and a filter medium 622, such as asorbent material, e.g., activated carbon, disposed within the housing620. An optical analyte sensor 628 is also disposed within the housing620 in fluid communication with the filter medium 622. As explainedabove, the optical analyte sensor 628 may include a detection mediumthat changes at least one of its optical characteristics in response toan analyte, and it is disposed within the housing 620 such that thedetection medium is in fluid communication with the filter medium 622. Awall 626 of a housing 620 includes a viewing port, such as a transparentportion 627 through which the optical analyte sensor 628 may beinterrogated.

The filter system 600 further includes a removable housing portion 630that is capable of being removably attached to the housing 620. Althoughin FIGS. 11A-11D the removable housing portion 630 is shown as astructure encircling the outer wall 626 of the housing 620, theremovable portion can take on a variety of other suitable shapes. Insome embodiments, the removable housing portion may be in the form of acollar or skirt, or a cover or cap. FIG. 12 shows an alternativeembodiment of a removable housing portion 635 according to the presentdisclosure, which is shaped as a cover or cap. An optical reader 655 maybe permanently or removably attached to the removable housing portion635. In other exemplary embodiments, the removable housing portion mayonly partially encircle or cover the housing, e.g., the removablehousing portion may encircle only a portion of the outer wall 626 of thehousing 620. Other configurations are also within the scope of thepresent disclosure.

The removable attachment of the housing portion 630 to the housing 620may be effectuated by any suitable attachment mechanism, such as one ormore resilient snap-fit features. FIG. 13A shows one exemplaryembodiment of an attachment mechanism 660, which includes one or moretabs 663 and one or more mating slots 662. Although the figure shows thetab being a part of the removable housing portion 630 and the slot beinga part of the housing 620, the location of the features could bereversed and changed in any suitable way. Another exemplary embodimentof an attachment mechanism is illustrated in FIGS. 12 and 13B. FIG. 12shows one or more (preferably, plurality) of beveled ribs 665, which areconfigured to be engaged by one or more (preferably, plurality) of hooks664. Other suitable attachment mechanisms may include one or morelatches (such as a latch described in connection with FIGS. 18A and18B), threaded features, or separate engagement parts such as screws,nuts or clips engaging the housing 620 and the housing portion 630.Thus, in some exemplary embodiments, when the filter cartridge isexpired, attachment features according to the present disclosure allowone to readily detach the removable housing portion and retain it foruse on succeeding filter cartridges. In other exemplary embodiments, thehousing portion 630 may be permanently attached, for example, byadhesive.

With further reference to FIGS. 11A to 11D, the filter system 600includes an optical reader 650. The optical reader, including itscircuitry and power source, can be permanently or removably attached tothe housing portion 630. The housing portion 630, in turn, may bepermanently or removably attached to the housing 620. As describedabove, the optical reader 650 may include at least one light source andat least one detector. The optical reader then should be attached to theremovable housing portion 630 such that, when the removable housingportion 630 is attached to the housing 620, at least a portion of lightemitted by at least one light source is reflected from the opticalanalyte sensor 628 and captured by at least one detector.

In the illustrated embodiment, the optical reader 650 is disposedbetween the removable housing portion 630 and the optical analyte sensor628. However, in other exemplary embodiments, some portions orcomponents of the optical reader 650 may be disposed outside of theremovable housing portion 630. For example, the removable housingportion 630 may include one or more openings 632 and 634. At least onesuch opening may be disposed over the optical reader 650. This may beuseful if the optical reader 650 includes an alerting device with avisual indicator visible through at least one of the openings.

In some exemplary embodiments, the optical reader 650 can be caused tointerrogate the optical analyte sensor 628, and, optionally, provide theabove-referenced indication, upon actuation by a user, such as via apush button. A user actuator (such as an actuator described inconnection with FIGS. 8A and 8B) operatively connected with the opticalreader may be accessible to a user through one of the openings 632 and634. Thus, in such exemplary embodiments, upon user actuation of theoptical reader 650, a spectrum of light captured by at least onedetector of the optical reader 650 can be analyzed for a change in atleast one of the optical characteristics of the detection medium of theoptical analyte sensor 628. The optical reader 650 can then provide anindication to a user if the change in at least one opticalcharacteristic meets a predetermined condition.

In typical embodiments of the present disclosure, with an optical readerhaving at least one light source and at least one detector, the opticalreader is attached (permanently or removably, via a housing portion ordirectly) to the housing of a filter system, such as a filter cartridge,such that at least a portion of light emitted by at least one lightsource is reflected from the optical analyte sensor and captured by atleast one detector. To aid in aligning the optical reader in such amanner, at least one of the optical reader and the housing or theremovable housing portion (whichever the optical sensor is disposed on)includes at least one registration feature. In typical embodiments ofthe present disclosure, each of the optical reader and the housing orremovable housing portion have a registration feature that mates with acorresponding feature on a connecting part.

In particular, FIGS. 11C and 11D show that a registration feature 652 ofthe optical reader 650 may be a slot, while a registration feature ofthe removable housing portion 630 may be a rib 636. As illustrated inFIG. 11D, the registration features 652 and 636 can be mated to achievea proper alignment of the optical reader 650 and the optical analytesensor 628, when the filter system 600 is assembled as shown in FIG.11B.

A variety of other types of registration features may be usedconsistently with the present disclosure, such as mating protrusion(s)and depression(s), tab(s) and slot(s), etc. For example, FIG. 14A showsan optical reader 750 having registration features 752 a and 752 b.Mating registration features, such as ribs (not shown) would be providedon a removable housing portion or the housing. Other configurations arealso within the scope of the present disclosure, including slots ofdifferent shapes and sizes, other types of depressions or protrusions,snaps, etc. FIG. 14B shows another exemplary embodiment of one or moreregistration features. In particular, optical reader 751 includes one,two or more posts 753 a, 753 b configured to mate with one, two or moreopenings 732 a, 732 b of a removable housing portion 730, a housingitself, of another suitable component. FIG. 14C shows another exemplaryembodiment of one or more registration features. In particular, FIG. 14Cillustrates a portion of an optical reader 755 including one or morerails 757 a, 757 b, and 757 c, which are configured to mate withcorresponding grooves 737 a, 737 b and 737 c of a removable housingportion 735, a housing itself, of another suitable component. Two, threeor more rails and the corresponding grooves may be different in size toensure that the orientation of the optical reader not be reversed. Forexample, as shown in FIG. 14C, rail 757 b is wider than rail 757 a, andrail 757 c is wider than rail 757 b.

Exemplary systems according to the present disclosure may furtherinclude a method or mechanism for confirming the alignment of theoptical reader with the optical analyte sensor before the filter systemis used. For example, once the optical reader is mounted onto a filtersystem such that the optical reader is over an optical analyte sensor,alignment can be diagnosed by determining how much light is received bythe detector, comparing it to a threshold value, and if the amount oflight received by the detector is below a certain threshold, the opticalreader may be deemed to be out of alignment. This feature can beaccomplished, for example, using an optical reader as illustrated inFIGS. 8A and 8B. In addition to the features described above, theoptical reader 500 would further include an alignment indicator (such asthe one or more indicators 516 and 518). Alternatively, separatealignment indicator(s) may be provided.

Generally, during a diagnostic sequence, light from one or more lightsources 512 and 514 would reflect off an alignment feedback feature (forexample, an optical analyte sensor under test according to any exemplaryembodiment) and be detected by the detector 520. Although the alignmentfeedback feature is exemplified as an optical analyte sensor, it canalso be a feature separate from (and additional to) an optical analytesensor, such as any specularly or diffusely reflective feature, forexample, a reflective or white film, tape, sticker or dot. The detectedsignals may be analyzed and compared to one or more predeterminedparameters or criteria indicative of proper alignment, such as theamount of light received by the detector and/or its spectralcharacteristics. The optical reader is then deemed to be out ofalignment, if the detected signals do not meet at least one criterionindicative of proper alignment.

In one embodiment, alignment indicator may provide an indication thatthe optical reader is disposed over an optical analyte sensor, such as ablinking light. The detector 520 would measure an amount of light fromboth light sources 512 and 514 reaching and reflected from the opticalanalyte sensor. If the optical reader is aligned properly, the detector520 would see responses for both light sources to be similar or of apredetermined ratio with a nominal error %. Alignment indicator may thenprovide an indication of proper alignment, for example, by stoppingblinking and turning on steady for few seconds. If the detector detectsthat a signal from one or both of light sources does not correspond to apredetermined value, an indication of misalignment will be provided. Forexample, alignment indicator may continue blinking rapidly. In otherexemplary embodiments, alignment testing may be performed with aseparate (additional) light source(s) and/or detector(s) than the lightsources 512, 514 and a detector 520.

FIG. 15 shows another embodiment of a filter system according to thepresent disclosure—a personal respirator 2 including a respiratorcartridge 23. The exemplary personal respirator 2 includes a face mask20 on which a pair of air purifying respirator cartridges 23 may bemounted, although the number of cartridges may vary. For example, someembodiments may include only one cartridge. One or more cartridges 23may be removable with respect to the face mask 20 and replaceable. Oneor more cartridges 23 includes a housing 22 and a filter medium 21(shown in FIG. 16), such as a sorbent material, e.g., activated carbon,disposed within the housing 22. An optical analyte sensor 28 includingdetection medium (not shown) is also disposed within the housing 22 suchthat the detection medium is in fluid communication with the filtermedium. The exemplary housing 22 includes a front cover 24 that has aplurality of openings 25 that may serve as gas inlets, permittingambient air from the external environment to flow into cartridge 23,through the filter medium and thence through a passage (not shown) thatserves as a gas outlet from cartridge 23 and an inlet to face mask 20.Exhaled air exits respirator 2 through an exhalation valve.

A wall 26 of a housing 22 may include a transparent portion 27 (which istransparent for the particular spectral range to which the lightsource(s) and the detector(s) are tuned) through which the opticalanalyte sensor 28 may be read by an optical reader 29. Alternatively,the entire wall 26 may be transparent. The optical analyte sensor 28 maybe included in one or more of the cartridges 23. As in the previouslydescribed embodiments, optical analyte sensor 28 is opticallyresponsive, for example, by undergoing a change when the filter mediumbecomes equilibrated with an analyte at the conditions of exposure. Inparticular, the detection medium of the optical analyte sensor maychange at least one of its optical characteristics in response to theanalyte, which change is detected by the optical reader. Thisinformation may be used in a variety of ways, including processing,storing, and communicating it to the wearer or another individual,possibly aiding such individual(s) in recognizing that it is time toreplace the cartridge or cartridges 23.

FIG. 16 is a side view, partially in section, of a respirator cartridge23. If desired, the openings 25 could be sealed until use using forexample a removable cover (not shown) that would be removed before use.A filter medium 21, such as bed of sorbent material, may absorb oradsorbs vapors of interest passing from the openings 25 to outlet 24. Asis common in such devices, one-way inhalation valve may be mounted on apost prevents exhaled air from entering cartridge 23. A threaded orpreferably bayoneted connector or connectors, such as those known tothose of ordinary skill in the art, can be used to removably couplecartridge 23 to the face mask 20. As described in connection with FIGS.1-3, the cartridge(s) 23 would be removed and replaced with freshcartridge(s) when a change in at least one optical characteristic of theoptical analyte sensor 28 indicates that the filter medium 21 underneaththe optical analyte sensor 28 has become equilibrated with the analyteat the conditions of exposure. The change may be used to indicate theremaining service life for the cartridge 23, the end of its servicelife, or to give warning at the desired remaining service lifepercentage.

FIGS. 17A and 17B show another exemplary filter system 800 according tothe present disclosure. In this exemplary embodiment, the exemplaryfilter system is a filter cartridge 800, which may be used in personalrespirators, such as a personal respirator 2 described in connectionwith FIG. 15. The filter cartridge 800 includes a housing 820 and afilter medium 822, such as a sorbent material, e.g., activated carbon,disposed within the housing 820. An optical analyte sensor 828 is alsodisposed within the housing 820 in fluid communication with the filtermedium 822. As explained above, the optical analyte sensor 828 mayinclude a detection medium that changes at least one of its opticalcharacteristics in response to an analyte, and it is disposed within thehousing 820 such that the detection medium is in fluid communicationwith the filter medium 822. A wall 826 of a housing 820 may include aviewing port, such as a transparent portion 827 through which theoptical analyte sensor 828 may be interrogated.

The filter system 800 further includes a removable housing portion 830that is capable of being removably attached to the housing 820. Theremovable attachment of the removable housing portion 830 to the housing820 may be effectuated by any suitable attachment mechanism, such as oneor more one or more resilient snap-fit features, such as those shown inFIGS. 18A and 18B. Thus, in some exemplary embodiments, when the filtercartridge is expired, a removable housing portion can be readily removedand retained by the user for use on succeeding filter cartridges. Othersuitable attachment mechanisms may include one or more latches, threadedfeatures, such as a circumferential thread, a bayonet-style lockingmechanism, separate engagement parts such as screws, nuts or clipsengaging the housing 820 and the housing portion 830. In other exemplaryembodiments, the housing portion 830 may be permanently attached, forexample, by adhesive.

The filter system 800 includes an optical reader 850. The opticalreader, including its circuitry and power source, can be permanently orremovably attached to the housing portion 830. The housing portion 830,in turn, may be permanently or removably attached to the housing 820. Asdescribed above, the optical reader 850 may include at least one lightsource and at least one detector. The optical reader then should beattached to the removable housing portion 830 such that, when theremovable housing portion 830 is attached to the housing 820, at least aportion of light emitted by at least one light source is reflected fromthe optical analyte sensor 828 and captured by at least one detector.The optical reader 850 may be disposed between the removable housingportion 830 and the optical analyte sensor 828, or some portions orcomponents of the optical reader 850 may be disposed outside of theremovable housing portion 830.

FIGS. 18A and 18B illustrate one suitable attachment mechanism that maybe used, for example, in a filter system 800. FIG. 18A shows theremovable housing portion 830 detached from the housing 820. In thisexemplary embodiment, the side wall of the housing 826 has a latchstructure 829 attached thereto. The latch structure 829 may include aprojection 829 a extending generally along the direction of the wall 826and a retaining member 829 b, projecting outwardly from the wall 826.The latch structure 829 is configured to engage a mating structure ofthe removable housing portion 830, such as a projection 833 of an edge832 of the removable housing portion, as shown in FIG. 17B.

Although in FIGS. 16A-16B and 17A-17B, the removable housing portion 830is shown as a structure encircling the outer wall 826 of the housing820, the removable portion can take on a variety of other suitableshapes (see, e.g., FIG. 18). Although in some embodiments, the removablehousing portion may be in the form of a collar or skirt, or a cover orcap, in other exemplary embodiments, the removable housing portion maycover only a portion of the outer wall of the housing.

Such a configuration is illustrated schematically in FIG. 19, whichshows an exemplary filter system 900 according to the presentdisclosure. The filter system 900 includes a housing 920. The filtersystem 900 further includes a removable U-shaped housing portion 930that is capable of being removably attached to the housing 920. Theremovable attachment of the removable housing portion 930 to the housing920 may be effectuated by forming the removable housing portion 930 forma resilient material, such that the ends 932 and 934 of the removablehousing portion operate as living hinges that each exerts a force on thehousing 920 thus retaining the removable housing portion in place. Othersuitable attachment mechanisms can also be used such as those describedabove in connection with other embodiments or any other suitableattachment mechanisms.

Exemplary embodiments including a removable housing portion (such as acollar or skirt) provide a convenient means of holding an optical readerin proximity to and in alignment with the optical analyte sensor that isincluded as a part of a respirator cartridge. In such exemplaryembodiments, the optical reader can be detached as desired from thecartridge housing and/or from the removable housing portion and replacedinto the assembly with highly reproducible positioning. The housingportion may also serve to mechanically protect the optical reader whilein use. If constructed from opaque plastic and/or coated with alight-absorbing material, various parts of the filter assembly mayprevents incoming light and thereby maintains consistent illuminationfor the optical reader.

It will be apparent to those skilled in the art that the specificexemplary structures, features, details, configurations, etc., that aredisclosed herein can be substituted, modified and/or combined innumerous embodiments. For example, optical readers and/or opticalanalyte sensors described herein may be used with a variety of filtersystems described herein or any other suitable filter systems. All suchvariations and combinations are contemplated by the inventors as beingwithin the bounds of the conceived invention. Thus, the scope of thepresent invention should not be limited to the specific illustrativestructures described herein, but rather by the structures described bythe language of the claims, and the equivalents of those structures. Tothe extent that there is a conflict or discrepancy between thisspecification and the disclosure in any document incorporated byreference herein, this specification will control.

This application is a continuation of U.S. patent application Ser. No.13/634,131, which was a national stage filing under 35 U.S.C. 371 ofPCT/US2011/030257, which claimed priority to Provisional ApplicationSer. No. 61/320,440 filed Apr. 2, 2010; the disclosures of all of whichare incorporated by reference in their entirety herein.

Examples 1. Optical Analyte Sensor Preparation

TABLE 2 Materials for PIMS Synthesis ABBREVIATION DESCRIPTION BCbis-catechol; 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane FA fluorinated arene;tetrafluoroterephthalonitrile DMF N,N-dimethylformamide THFtetrahydrofuran

An optical analyte sensor of this example was a thin film indicator asdepicted in FIG. 3A. It was prepared using a polymer of intrinsicmicroporosity (PIM) as the detection layer, a Ni partially reflectivelayer, and a silver nanoparticle vapor-permeable reflective layer. PIMpolymer was prepared from the monomers BC and FA generally according tothe procedure reported by Budd et al. in Advanced Materials, 2004, Vol.16, No. 5, pp. 456-459. 9.0 grams of BC were combined with 5.28 g of FA,18.0 g potassium carbonate, and 120 milliliters of DMF and the mixturewas reacted at 70° C. for 24 hours. The resulting polymer was dissolvedin THF, precipitated three times from methanol, and then dried undervacuum at room temperature (PIM Sample 50-2).

A metalized polyethylene terephthalate (PET) substrate was prepared byevaporatively depositing a 10 nm-thick Ni metal onto Melinex ST505 clearPET. The PIM polymer was dissolved at 4% concentration in chlorobenzeneand solution deposited onto a base substrate consisting of Ni-coatedPET.

Finally, a silver nanoparticle layer was deposited onto the PIM. 100 gof stock nanosilver solution (DGP-40LT-15C from Advanced Nanoproducts,Korea, 40 wt % silver) was diluted with 150 g of 1-methoxy-2-propanoland coated onto the PIM layer. After deposition, the overall sensorconstruction was heated at 130 Celsius for 12 hr to sinter the silvernanoparticles.

2. Filter Cartridge Preparation

A respirator cartridge was prepared by first adhering a 12 mm×25 mmpiece of sensor film (described in Example 1) to the inner wall of aclear polycarbonate cartridge body using transfer adhesive (8172, 3MCompany, St. Paul, Minn.). The cartridge body was then filled with 800cc of Kuraray GC carbon (12×20 mesh size) and a retainer plate wasultrasonically welded to the body to contain the carbon and close thecartridge. The construction of the cartridge is shown in FIG. 2.

3. Optical Reader and Housing Preparation

To electronically interrogate the film sensor within the respiratorcartridge, an optical reader containing two surface mount light emittingdiodes (LED's) and a silicon photodetector was prepared. The detectionoptics i.e. LEDs and detector were mounted on the opposite sides of theprinted circuit board with a cavity in the board. Light from the LEDsreflects off the film and irradiates the detector. This constructionpermits the reader to have a thin form factor and also prevents directinterference from the LEDs. The LED's were chosen with peak emissionwavelengths of 591 nm and 606 nm. The reader functions by irradiatingthe sensor at these selected wavelengths in succession. The reflectedlight intensity is measured by the photodetector to determine the sensorresponse based on shifts in its visible reflectance spectrum.

A clear plastic housing was created using stereolithography (SLA) tohouse the optical reader. Clear resin from DSM Somos (Watershed 11120)was used to create the cassette. Such a reader is shown in FIG. 8.

4. Cartridge Skirt to House a Detachable Optical Reader

A plastic skirt for the respirator cartridge shown in FIG. 10D wascreated in black ABS resin. Shown in FIGS. 10A-10D are the skirt and itsuse in holding the detachable reader in proximity of the sensor.Although the skirt is depicted as detachably couplable to the filtercartridge, in this embodiment the skirt would likely be permanentlyattached to the filter with the reader detachably connected to thefilter/skirt assembly. Used in this fashion, the skirt provides a robustmeans of attaching the reader and also protects the reader frommechanical abuse or from contamination (dust, mist, spray) within aworking environment. The reader was attached to the skirt using a doublesided adhesive tape.

5. Detachable Cartridge Skirt

This embodiment is similar to Example 4, but here the reader ispermanently attached to the skirt, creating an assembly which can beremovably coupled with the filter system. Use of a reader/skirt assemblyminimizes chances of losing the reader during use, eliminates handlingof the bare reader cartridge, and makes the overall system more robust.

6. Detachable Skirt or Sleeve for Cartridges that are Suitable forReusable Negative Pressure respirators

This embodiment is similar to Example 5, but tailored to be used withthe respirator cartridges for reusable negative pressure respirators.The reader is permanently attached to a skirt or sleeve which can beremovably coupled with the cartridge. The user would remove and attachthe reader/skirt assembly from the cartridge. This minimizes chances oflosing the reader during use, eliminates handling of the bare readercartridge, and makes the overall system more convenient to assemble anduse. Such a device is expected to have the optical reader integratedinto the collar and housed in a protective case with a see-throughcavity to read the film on the cartridge.

What is claimed is:
 1. A filter system comprising: a housing; a filtermedium disposed within the housing; an optical analyte sensorcharacterized by a first region that exhibits a first response to ananalyte of interest and a second region that exhibits a second,different, response to an analyte of interest, the optical analytesensor comprising a detection medium and disposed within the housingsuch that the detection medium is in fluid communication with the filtermedium; and an optical reader comprising a first assembly comprising atleast one light source and at least one detector and a second assemblycomprising at least one light source and at least one detector; whereinthe optical reader is attached to the housing such that at least aportion of light emitted by at least one light source of the firstassembly is reflected from the first region of the optical analytesensor and captured by at least one detector of the first assembly, andat least a portion of light emitted by at least one light source of thesecond assembly is reflected from the second region of the opticalanalyte sensor and captured by at least one detector of the secondassembly.
 2. The filter system of claim 1, wherein the housing comprisesa removable housing portion and the optical reader is attached to theremovable housing portion.
 3. The filter system of claim 1, wherein theoptical analyte sensor comprises an occluding layer and the first regioncorresponds to an area masked by the occluding layer.
 4. The filtersystem of claim 1, wherein the optical reader comprises at least oneregistration feature.
 5. The filter system of claim 1, wherein a signalfrom the detector of the first assembly is compared to a signal from thedetector of the second assembly.
 6. A filter system comprising: ahousing; a filter medium disposed within the housing; an optical analytesensor characterized by a first region that exhibits a first response toan analyte of interest and a second region that exhibits a secondresponse to the analyte of interest, the optical analyte sensorcomprising a detection medium and disposed within the housing such thatthe detection medium is in fluid communication with the filter medium;and an optical reader comprising a first assembly comprising a firstblock, the first block comprising a first light source and a firstdetector, and a second block, the second block comprising a second lightsource and a second detector, and a second assembly comprising a lightsource and a detector; wherein the optical reader is disposed such thatat least a portion of light emitted by the first light source of thefirst assembly is reflected from a first area of the first region of theoptical analyte sensor and captured by the first detector, at least aportion of light emitted by the second light source of the firstassembly is reflected from a second, different, area of the first regionof the optical analyte sensor and captured by the second detector, andat least a portion of light emitted by at least one light source of thesecond assembly is reflected from the second region of the opticalanalyte sensor and captured by at least one detector of the secondassembly.
 7. The filter assembly of claim 6, wherein the first assemblycomprises the third block, the third block comprising a third lightsource and a third detector, and wherein the optical reader is disposedsuch that at least a portion of light emitted by the third light sourceof the third assembly is reflected from a third area, different from thefirst and second area, of the first region of the optical analyte sensorand captured by the third detector.
 8. The filter system of claim 6,wherein the housing comprises a removable housing portion and theoptical reader is attached to the removable housing portion.
 9. Thefilter system of claim 6, wherein the optical reader is removablyattached to the housing.
 10. The filter system of claim 6, wherein theoptical reader comprises at least one registration feature.
 11. Thefilter system of claim 6, wherein a signal from the detector of thefirst assembly is compared to a signal from the first and seconddetectors to a signal from the detector of the second assembly.
 12. Afilter system comprising: a housing; a filter medium disposed within thehousing; an optical analyte sensor characterized by a first region thatexhibit a first response to an analyte of interest and a second regionthat exhibit a second, different, response to an analyte of interest,the optical analyte comprising a detection medium and disposed withinthe housing such that the detection medium is in fluid communicationwith the filter medium; and an optical reader comprising at least onelight source and at least one detector; wherein the optical reader isconfigured to be disposed such that at least a portion of light emittedby at least one light source is reflected from the first region of theoptical analyte sensor and captured by at least one detector, andwherein at least a portion of light emitted by at least one light sourceis reflected from the second region of the optical analyte sensor andcaptured by at least one detector.
 13. The filter system of claim 12,wherein the optical analyte sensor comprises an occluding layer and thefirst region corresponds to an area masked by the occluding layer. 14.The filter system of claim 12, wherein the optical reader comprises onelight source and one detector.
 15. The filter system of claim 12,wherein the housing comprises a removable housing portion and theoptical reader is attached to the removable housing portion.
 16. Thefilter system of claim 12, wherein the optical reader is removablyattached to the housing.